Recently, there have been used filter elements comprising a porous body as a filter medium for removing suspended materials, bacteria and dusts in liquid in a wide variety of the fields such as of water treatment, medicine and food.
Porous bodies of various shapes are used as the above filter elements depending on the purpose of filtration, and, for example, a filter element 2 as shown in FIG. 2 is generally used which has a substrate comprising a cylindrical porous body having many pores and having a plurality of cells 3 which are flow paths for untreated liquid (hereinafter, such a shape is sometimes referred to as “monolithic”) and a filtering membrane comprising a porous body which has an average pore diameter smaller than that of the substrate and is formed on the inner wall of a plurality of the cells 3.
In the above-mentioned monolithic filter element, when an untreated liquid (a liquid to be treated) is supplied into a plurality of the cells under a given pressure, the liquid permeates through the filtering membrane formed on the inner wall of the cells and the porous body constituting the substrate and is discharged through the outer peripheral surface of the substrate, during which the suspended material is entrapped by the filtering membrane. Therefore, the purified liquid can be recovered by employing a structure where the filter element is contained in the casing in such a state that the outer peripheral surface side and the cell opening end face side of the substrate are liquidtightly separated from each other by a sealer. Furthermore, since the average pore diameter of the filtering membrane (about 0.01-1.0 μm) is made smaller than that of the substrate (1-several hundred μm), the filtering performance is assured and, besides, the flow resistance at the time of the permeation of liquid through the porous body constituting the substrate can be reduced and thus the fluid permeation amount (namely, throughput capacity) can be improved.
The monolithic filter elements mentioned above can be used each alone, but when a large amount of untreated liquid (untreated water) is required to be treated as in the case of water treatment plant, many filter elements are connected to increase the filtration area and improve the throughput capacity.
As a filter comprising many filter elements which are connected, there is known, for example, a filter in which many filter elements are contained in a casing in such a state that they are supported by piercing both ends of the filter elements through an upper plate and a lower plate, respectively, and they are arranged in parallel (see, for example, JP-A-10-180049).
However, if it is attempted to improve the throughput capacity by increasing the number of the filter elements to be connected to increase the filtration area, the installing area of the filter must be increased in proportion to the number of the filter elements and the throughput capacity per installing area of the filter is small.